Blood pressure measurement apparatus and blood pressure measurement method

ABSTRACT

In an ultrasound blood pressure monitor, a blood pressure diameter measurement section measures blood pressure diameter of a radial artery which is a measurement target based on reception results of ultrasound from an ultrasound sensor. In addition, a pressurizing section adds a pressure from a body surface so that the radial artery is pressed. Then, a correlation formula, which expresses a relationship between blood vessel diameter and blood pressure of the radial artery under pressurization by the pressurizing section, is found and stored in a storage section. Then, a blood pressure calculation section calculates blood pressure using the blood vessel diameter which is measured under pressurization and storage data in the storage section by controlling the pressurization operation of the pressurizing section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2011-273629 filed on Dec. 14, 2011 and Japanese Patent Application No.2012-226666 filed on Oct. 12, 2012. The entire disclosure of JapanesePatent Application Nos. 2011-273629 and 2012-226666 is herebyincorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to an apparatus, which measures bloodpressure of a patient, and the like.

2. Background Technology

From the related art, an apparatus which measures blood flow, bloodvessel diameter, and blood pressure using ultrasound or the like and anapparatus which measures elasticity of a blood vessel have beenproposed. These apparatuses have a characteristic in that measurement ispossible without imparting pain or an unpleasant feeling to the patient.

For example, a technique is disclosed in Patent Document 1 where changesin blood pressure and changes in blood vessel diameter are assumed tohave a non-linear relationship and blood pressure is calculated from ablood vessel elasticity index called a stiffness parameter and from theblood vessel diameter.

Japanese Laid-open Patent Publication No. 2004-41382 (Patent Document 1)is an example of the related art.

SUMMARY Problems to Be Solved by the Invention

The technique which is disclosed in PTL1 is a technique where bloodpressure is calculated based on correlation characteristics of bloodvessel diameter and blood pressure. However, in an artery which iscomparatively thin such as a limb artery, variation in the blood vesseldiameter with regard to the change in blood pressure is extremely slightsince the blood vessel is hard.

For example, in a radial artery which flows in the wrist, the change inblood vessel diameter is approximately 40 [μm] in relation to a changein blood pressure accompanying a pulsation which is approximately 50[mmHg]. Accordingly, a blood vessel diameter measurement method, wheremeasurement in units of a minimum of 8 [μm] is possible, is required inorder to calculate blood pressure with, for example, a degree ofaccuracy of 10 [mmHg]. However, it is considered that a blood vesseldiameter measurement method which realizes this degree of accuracy isdifficult to realize.

The invention is carried out in consideration of the problems describedabove and has an advantage of proposing a novel technique for improvingthe degree of accuracy in blood pressure calculation.

Means Used to Solve the Above-Mentioned Problems

A first embodiment which solves the problems above is a blood pressuremeasurement apparatus which is provided with a blood vessel diametermeasurement section which measures blood vessel diameter of an arterywhich is a measurement target, a pressurizing section which addspressure from a body surface so that the artery is pressed, a storagesection which stores a relationship between blood vessel diameter andblood pressure of the artery under pressurization by the pressurizingsection, and a blood pressure calculation section which calculates bloodpressure by controlling a pressurization operation of the pressuringsection using the blood vessel diameter, which is measured by the bloodvessel diameter measurement section under pressurization, and storagedata in the storage section.

In addition, as another embodiment, a blood vessel diameter measurementmethod for a blood vessel diameter measurement apparatus which isprovided with a pressurizing section which adds pressure from a bodysurface so that an artery which is a measurement target is pressed and astorage section which stores the relationship between blood vesseldiameter and blood pressure of the artery under pressurization by thepressurizing section, the method including measuring blood vesseldiameter of the artery, and calculating blood pressure by controlling apressurization operation of the pressuring section using the bloodvessel diameter under pressurization and storage data in the storagesection.

According to the first embodiment, the blood vessel diameter of theartery which is the measurement target is measured. Along with this, thepressurizing section adds pressure from the body surface so that theartery is pressed. Then, the relationship between the blood vesseldiameter and the blood pressure of the artery under pressurization bythe pressurizing section is stored and the blood pressure is calculatedby controlling the pressurization operation of the pressuring sectionusing the blood vessel diameter which is measured under pressurization,and the storage data in the storage section. According to experimentswhich were performed by the present inventors, the variation width inthe blood vessel diameter with regard to the same change in bloodpressure increases when pressure is added from the body surface so thatthe artery is pressed compared to when there is no pressurization.Accordingly, it is possible to reduce the effect of blood vesseldiameter measurement errors by using pressurization and it is possibleto improve the degree of accuracy in the blood pressure calculation.

In addition, as a second embodiment, the blood pressure measurementapparatus in the blood pressure measurement apparatus of the firstembodiment can be a configuration where there is further provided afirst pressure search section which searches for a pressure bycontrolling the pressure due to the pressurizing section so as to changeso that the variation width in the blood vessel diameter accompanying apulsation, which is measured by the blood vessel diameter measurementsection, satisfies a predetermined condition, the storage section storesthe relationship between the blood vessel diameter and the bloodpressure of the artery in a state of pressurization with the pressurewhich has been searched for by the first pressure search section, andthe blood pressure calculation section controls the pressurizationoperation of the pressurizing section so that there is pressurizationwith the pressure which is searched for by the first pressure searchsection.

According to the second embodiment, the pressure is searched for by thefirst pressure search section by controlling the pressure due to thepressurizing section so as to change so that the variation width in theblood vessel diameter accompanying a pulsation, which is measured by theblood vessel diameter measurement section, satisfies the predeterminedcondition. On top of this, the relationship between the blood vesseldiameter and the blood pressure of the artery, which is in a state ofpressurization with the pressure which has been searched for by thefirst pressure search section, is stored in the storage section. Theblood pressure calculation section controls the pressurization operationof the pressurizing section so that there is pressurization with thepressure which has been searched for by the first search section. Therelationship between the blood vessel diameter and the blood pressure ina case of pressurization with the pressure which has been searched foris stored as data and it is possible to correctly calculate the bloodpressure of a patient by calculating the blood pressure by referencingthe blood vessel diameter which is measured in a state of pressurizationwith a pressure which is the same as this and the storage data in thestorage section.

In addition, as a third embodiment, the blood pressure measurementapparatus in the blood pressure measurement apparatus of the secondembodiment can be a configuration where the first pressure searchsection searches for a pressure where the variation width of the bloodvessel diameter accompanying a pulsation, which is measured by the bloodvessel diameter measurement section, exceeds a predetermined variationwidth threshold which is set based on the relationship between pulsepressure and the variation width.

According to the third embodiment, it is possible to adjust the pressurewhich is pressurized by the pressurizing section due to the firstpressure search section searching for a pressure where the variationwidth of the blood vessel diameter accompanying a pulsation, which ismeasured by the blood vessel diameter measurement section, exceeds apredetermined variation width threshold which is set based on therelationship between pulse pressure and the variation width.

In addition, as a fourth embodiment, the blood pressure measurementapparatus in the blood pressure measurement apparatus of any of thefirst to the third embodiments can be a configuration where the bloodpressure calculation section controls the pressurization operation ofthe pressurizing section so as to pressurize with an arbitrary pressure.

According to the fourth embodiment, the pressurization operation of thepressurizing section is controlled so as to pressurize with an arbitrarypressure at a time when calculating the blood pressure. It is possibleto increase variation in the blood vessel diameter as the pressureincreases and it is possible to improve the degree of accuracy in bloodpressure calculation. Accordingly, it is possible to calculate the bloodpressure with an arbitrary setting of the pressure in order to securethe degree of accuracy in blood pressure calculation.

In addition, as a fifth embodiment, the blood pressure measurementapparatus in the blood pressure measurement apparatus of the fourthembodiment can be a configuration where there is further provided asecond pressure search section which searches for a pressure bycontrolling the pressurization by the pressurizing section so as tochange so that the blood vessel diameter which is measured by the bloodvessel diameter measurement section satisfies a predetermined stabilitycondition, and the blood pressure calculation section controls thepressurization of the pressurizing section so that there ispressurization with the pressure which is searched for by the secondpressure search section.

For example, there is a possibility that a considerable error isincluded in the blood pressure calculation results in a case where thereis large dispersion in the blood vessel diameter which is measured in astate of pressurization with a certain pressure. Therefore, according tothe fifth embodiment, a pressure is searched for by controlling thepressurization by the pressurizing section so as to change so that theblood vessel diameter which is measured by the blood vessel diametermeasurement section satisfies a predetermined stability condition. Then,the blood pressure calculation section controls the pressurizationoperation of the pressurizing section so that there is pressurizationwith the pressure which has been searched for. Due to this, thepressurization force of the pressurizing section is adjusted at a timewhen calculating the blood pressure during normal measurement and it ispossible to improve the degree of accuracy in blood pressurecalculation.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1A is a configuration diagram of a blood pressure measurementsystem, and FIG. 1B is a diagram illustrating a mounting state of anultrasound blood pressure monitor;

FIG. 2 is a cross sectional diagram of a state where an ultrasound bloodpressure monitor is mounted on a wrist;

FIG. 3 is experiment results illustrating a relationship between apressurization force and blood vessel diameter variation width;

FIG. 4 is an explanatory diagram of correlation characteristics of bloodvessel diameter and blood pressure;

FIG. 5 is a block diagram illustrating an example of a functionalconfiguration of an ultrasound blood pressure monitor;

FIG. 6 is a flow chart illustrating the flow of a main process;

FIG. 7 is a flow chart illustrating the flow of a correction process;

FIG. 8 is a diagram illustrating an example of a configuration of ablood pressure measurement system according to a second embodiment;

FIG. 9 is a diagram illustrating changes in blood vessel diametervariation width;

FIG. 10 is a diagram for describing effects of a blood pressuremeasurement method in the second embodiment; and

FIG. 11 is a flow chart illustrating the flow of a second main process.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As an embodiment where the invention is applied, an embodiment of ablood flow measurement apparatus which measures blood pressure of apatient will be described with the wrist of a patient as a measurementtarget portion and an artery which is the measurement target as theradial artery. Here, naturally, the embodiments where it is possible forthe invention to be applied are not limited to the embodiments describedbelow.

1. Schematic Configuration

FIG. 1A is a configuration diagram of a system according to bloodpressure measurement of the embodiment. The blood pressure measurementsystem is configured to have an ultrasound blood pressure monitor 1which is configured to be able to be used by a patient mounting such ontheir wrist and a cuff type blood pressure monitor 3 which is used bybeing wrapped around the upper arm of a patient.

The cuff type blood pressure monitor 3 measures the blood pressure of anartery in the upper arm by the cuff which senses blood pressure beingwrapped around the upper arm of the patient. In the embodiment, the cufftype blood pressure monitor 3 is used in order to perform correction ofthe ultrasound blood pressure monitor 1. After the correction has beenperformed, the cuff type blood pressure monitor 3 is removed andmeasurement of blood pressure is performed using the ultrasound bloodpressure monitor 1 as a unit.

The ultrasound blood pressure monitor 1 is configured so that a bodysection is able to be mounted onto a measurement target portion (inparticular, a wrist) of the patient using a strip section 15. The stripsection 15 is a mounting tool for mounting an apparatus body onto themeasurement target portion of the patient and is configured to have aband which is provided with a surface fastener, a clip which is forpinching a gauging section, and the like. The body section of theultrasound blood pressure monitor 1 is configured to be connected to afirst portion 1A and a section portion 1B via a hinge section 11.

An operation button 12, a liquid crystal display device 13, and aspeaker 14 are provided in the first portion 1A.

The operation button 12 is used for the patient to operate and inputstarting instructions for the measurement of blood pressure and varioustypes of amounts which are related to the measurement of blood pressure.

The blood pressure measurement results according to the ultrasound bloodpressure monitor 1 are displayed in the liquid crystal display device13. As the display method, a blood pressure measurement value can bedisplayed using a numerical value or there can be a display using agraph or the like.

There is audio output such as various types of voice guidance which arerelated to the measurement of blood pressure from the speaker 14. In theembodiment, measurement of blood pressure using the cuff type bloodpressure monitor 3 is necessary in response to execution of a correctionprocess. As a result, there can be audio output of voice guidance, whichinstructs the attaching and removal of the cuff type blood pressuremonitor 3, from the speaker 14.

A sensor section 20 is provided in the second portion 1B. The sensorsection 20 is configured to have an ultrasound sensor 21 and apressurizing section 30.

The ultrasound sensor 21 is an ultrasound sending and receiving sectionwhere ultrasound oscillation units are lined up in an array formation.The ultrasound sensor 21 transmits a pulse signal or a burst signal ofultrasound of several MHz to several tens of MHz from a transmissionsection toward the measurement target blood vessel. Then, reflectedwaves from a front wall and a back wall of a measurement target bloodvessel are received by a reception section and the blood vessel diameteris measured at the measurement target blood vessel from a reception timedifference of the reflected waves of the front wall and the back wall.

As shown in FIG. 2, the pressurizing section 30 is a pressurizingmechanism which is configured to have a cylindrical cam mechanism and isconfigured to be disposed directly above the ultrasound sensor 21. Thepressurizing section 30 performs pressurization from directly above theultrasound sensor 21 in a state where the ultrasound blood pressuremonitor 1 is mounted on the measurement target portion and the bodysurface which is in contact with the ultrasound sensor 21 ispressurized.

Here, although omitted in the diagrams, a control substrate forcomprehensively controlling the device is built into the body section ofthe ultrasound blood pressure monitor 1. A microprocessor, a memory, acircuit which is related to the sending and receiving of ultrasound, abuilt-in battery, and the like are mounted in the control substrate.

FIG. 1B is a diagram illustrating a state where the ultrasound bloodpressure monitor 1 is mounted onto the left wrist of the patient. Asshown in FIG. 1B, the ultrasound blood pressure monitor 1 is mountedonto the wrist of the patient with a positioning so that the bodysection is directed to the inner side of the wrist. At this time, thesecond portion 1B where the sensor section 20 is provided is mounted soas to come to a position on the thumb side of the wrist of the patient.This is so that the sensor section 20 is positioned directly above thiswith the measurement target blood vessel as the radial artery wherethere is flow to the thumb side of the wrist.

FIG. 2 is a cross sectional diagram of a state where the ultrasoundblood pressure monitor 1 is mounted on a wrist. Here, an external coverof the body section is omitted in the diagram so that it is possible torecognize the inner portion of the apparatus in FIG. 2.

In the pressurizing section 30, a transmission gear 33 is rotated and aworm gear 34 which screws together with the transmission gear 33 isrotated due to an electromagnetic motor 32 being rotated by receivingelectric power from a power source section 40. Accompanying this, theprotrusion amount of the cylindrical cam mechanism 36 is controlled dueto the rotating of a worm gear wheel 35 and there is a formation where apressurizing plate 37 and a sensor water bag (pressure sensor) 38 arepushed out to the wrist side due to an increase in the protrusionamount.

The ultrasound sensor 21 is provided directly below the sensor water bag38. The ultrasound sensor 21 is pressurized toward the body surface atthe wrist due to the pushing out of the sensor water bag 38. That is,the ultrasound sensor 21 pressurizes the body surface directly above aradial artery A. The radial artery A changes shape due to thepressurization. In the embodiment, there is a characteristic whereultrasound is transmitted from the ultrasound sensor 21 in a state wherethe shape of the radial artery A has changed and the blood vesseldiameter of the radial artery A is calculated based on the reflectedwave.

2. Principles

FIG. 3 is a graph illustrating the extent to which the blood vesseldiameter variation width changes in accompaniment with a pulsation.Experiments, where the blood vessel diameter variation widthaccompanying a pulsation is measured, were performed while changing thepressurization force with regard to the radial artery with a pluralityof patients as targets. In FIG. 3, the horizontal axis is pressurizationforce and the vertical axis is blood vessel diameter variation width.The plotting formations are different for each patient. From theexperiments, it was understood that the blood vessel diameter variationwidth increases in accompaniment with an increase in the pressurizationforce.

FIG. 4 is a diagram illustrating the extent to which correlationcharacteristics of blood vessel diameter and blood pressure change whenthere is pressurization and no pressurization with regard to the radialartery. In the embodiment, the correlation characteristics of bloodvessel diameter “D” and the blood pressure “P” are approximated using anon-linear correlation formula which is expressed by the followingformula (1).

P=Pd·exp[β(D/Dd−1)]  (1)

Here, β=In(Ps/Pd)/(Ds/Dd−1)

In formula (1), “Ps” is contraction phase blood pressure (maximum bloodpressure) and “Pd” is extension phase blood pressure. In addition, “Ds”is contraction phase blood vessel diameter which is the blood vesseldiameter when there is the contraction phase blood pressure and “Dd” isextension phase blood vessel diameter which is the blood vessel diameterwhen there is the extension phase blood pressure. In addition, “β” is ablood vessel elasticity index called a stiffness parameter.

The graph in FIG. 4 is a graph which is formed in accordance withformula (1), the curve shown with the dotted line shows the correlationformula of blood vessel diameter “D” and the blood pressure “P” whenthere is no pressurization, and the curve shown with the solid lineshows the correlation formula of blood vessel diameter “D” and the bloodpressure “P” when there is pressurization. When viewing the graph, it isunderstood that the slope of the curve is smaller when there ispressurization compared to when there is no pressurization. That is, theblood vessel diameter variation width is larger with regard to the samechange in blood pressure when there is pressurization.

When specific numerical values are exemplified, the amount of variationin blood vessel diameter is approximately 200 [μm] with regard to achange in blood pressure of approximately 60 [mmHg] in a case where thebody surface is pressurization by 50 [mmHg], compared to there beingonly a change in blood vessel diameter of approximately 50 [μm] withregard to a change in blood pressure of approximately 60 [mmHg] whenthere is no pressurization. Accordingly, when the degree of accuracy ofblood vessel diameter measurement is the same, error in the blood vesseldiameter measurement is “approximately ¼” when there is pressurization.As a result, it is possible to improve the degree of accuracy in bloodpressure calculation.

Based on this insight, in the embodiment, a pressure, where thevariation width of the blood vessel diameter accompanying a pulsationmeasured using ultrasound satisfies a predetermined threshold, issearched for by controlling the pressurization by the pressurizingsection 30 so as to change. Then, the correlation formula of the bloodvessel diameter and the blood pressure of the radial artery in a stateof pressurization by the pressurizing section 30 with the pressure isfound and stored in a storage section. During measurement of bloodpressure, the blood pressure “P” of the patient is calculated using theblood vessel diameter “D”, which is measured using ultrasound in a stateof controlling the pressurization so that the pressurizing section 30pressurized with the pressure which is stored in the storage section,and the correlation formula which is stored in the storage section.

3. Functional Configuration

FIG. 5 is a block diagram illustrating an example of a functionalconfiguration of the ultrasound blood pressure monitor 1. The ultrasoundblood pressure monitor 1 is configured to have the sensor section 20, aprocessing section 100, an operating section 200, a display section 300,an audio output section 400, a communication section 500, a timersection 600, and a storage section 800.

The sensor section 20 is provided with the ultrasound sensor 21 and thepressurizing section 30. The ultrasound sensor 21 is an ultrasoundsending and receiving section and is configured to have an ultrasoundsending and receiving circuit. The ultrasound sending and receivingcircuit sends and receives ultrasound by, for example, switching betweenan ultrasound transmission mode and an ultrasound reception mode with atime division method in accordance with a sending and receiving controlsignal which is output from the sending and receiving control section120.

The sending and receiving circuit is configured to have an ultrasoundoscillation circuit which generates a pulse signal with a predeterminedfrequency, a transmission delay circuit which delays the pulse signalwhich has been generated, and the like as a transmission configuration.In addition, the sending and receiving circuit is configured to have areception delay circuit which delays a reception signal, a filter whichextracts a predetermined frequency component from the reception signal,an amplifier which amplifies the reception signal, and the like as aconfiguration for reception.

The processing section 100 is a control apparatus and a computationapparatus which comprehensively controls each section of the ultrasoundblood pressure monitor 1 and is configured to have, for example, amicroprocessor such as a CPU (Central Processing Unit) or a DSP (DigitalSignal Processer), an ASIC (Application Specific Integrated Circuit),and the like.

The processing section 100 has the sending and receiving control section120, a blood vessel diameter calculation section 130, a pressurizationcontrol section 140, a correction section 150, and a blood pressurecalculation section 160 as the main functional sections. Here, thesefunctional section are only a description of one example and it is notnecessary the case that all of these functional sections are essentialconfiguration elements.

The sending and receiving control section 120 controls the sending andreceiving of ultrasound by the ultrasound sensor 21. Specifically, asending and receiving control signal is output with regard to theultrasound sensor 21 and control of switching between the transmissionmode and the reception mode described above is performed

The blood vessel diameter calculation section 130 calculates the bloodvessel diameter of the measurement target blood vessel based on signalprocessing results which are input from the ultrasound sensor 21.Specifically, the blood vessel diameter of the measurement target bloodvessel is calculated by detecting a reception time difference of thereflected ultrasound waves of the front wall and the back wall of themeasurement target blood vessel.

In the embodiment, a blood vessel diameter measurement section 110 whichmeasures the blood vessel diameter of the artery which is themeasurement target (the radial artery) is configured by the ultrasoundsensor 21, the sending and receiving control section 120, and the bloodvessel diameter calculation section 130.

The pressurization control section 140 controls the pressurization bythe pressurizing section 30 with regard to the measurement targetportion. Specifically, the measurement target portion is pressurized bya predetermined pressurization force by outputting a pressurizationcontrol signal with regard to the pressurizing section 30. In theembodiment, a pressurization setting 821 of the pressurizing section 30is decided on in a correction process which is performed by thecorrection section 150.

The correction section 150 performs correction of the ultrasound bloodpressure monitor 1 at an initial correction after the power is turned onor a predetermined correction timing in accordance with a correctionprogram 811 which is stored in the storage section 800. The correctionsection 150 has a pressure search section 151 which carries out afunction of a first pressure search section which searches for apressure where the variation width of the blood vessel diameteraccompanying a pulsation, which is measured by the blood vessel diametermeasurement section 110, satisfies a predetermined condition.

The blood pressure calculation section 160 calculates the blood pressureof the patient using the blood vessel diameter which is measured by theblood vessel diameter measurement section 110 and the correlationformula which indicates the correlation characteristics of blood vesseldiameter and blood pressure. In the embodiment, a correlation formula823 is decided on in the correction process which is performed by thecorrection section 150.

The operating section 200 is an input apparatus which is configured tohave a button switch and the like and a signal of a button which hasbeen pressed is output to the processing section 100. Due to theoperation of the operating section 200, the input of various types ofinstructions such as an instruction for the starting of measurement ofblood vessel diameter is carried out. The operating section 200 isequivalent to the operation button 12 in FIG. 1.

The display section 300 is a display apparatus which is configured tohave an LCD (Liquid Crystal Display) or the like and performs varioustypes of display based on a display signal which is input from theprocessing section 100. Information such as the blood pressure which iscalculated by the blood pressure calculation section 160 is displayed inthe display section 300. The display section 300 is equivalent to theliquid crystal display unit 13 in FIG. 1.

The audio output section 400 is an audio output apparatus which performsvarious types of audio output based on an audio output signal which isinput from the processing section 100. The audio output section 400 isequivalent to the speaker 14 in FIG. 1.

The communication section 500 is a communication apparatus for sendingand receiving information which is used in the apparatus to and from anexternal information processing apparatus in accordance with the controlof the processing section 100. As the communication method of thecommunications section 500, it is possible to apply various methods suchas a format where a cable which complies with a predeterminedcommunication standard is connected in a wired manner, a format wherethere is connection via an intermediate apparatus which is also used asa recharger referred to as a cradle, a format where wirelesscommunication is performed using short-distance wireless communication,or the like. In the embodiment, the communication section 500 performsthe sending and receiving of data with the cuff type blood pressuremonitor 3 using short-distance wireless communication.

The timer section 600 is a timer apparatus which is configured to have acrystal oscillator, which is formed by a crystal resonator and anoscillator circuit, or the like and measures time. The time measuring ofthe timer section 600 is output at any time to the processing section100.

The storage section 800 is configured to have a storage apparatus suchas a ROM (Read Only Memory), a flash ROM, a RAM (Random Access Memory),or the like. The storage section 800 stores a system program of theultrasound blood pressure monitor 1, various types of programs forrealizing each of the functional sections of the sending and receivingcontrol function, the blood vessel diameter measurement function, andthe blood pressure calculation function, data, and the like. Inaddition, there is a work area which temporarily stores processing dataof various types of processing, processing results, and the like.

A main program 810, which is read out by the processing section 100 andis executed as a main process (refer to FIG. 6), is stored in thestorage section 800 as a program. The main program 810 includes thecorrection program 811 which is executed as the correction process(refer to FIG. 7) as a subroutine. This process will be described laterin detail using a flow chart.

In addition, correction data 820, the blood vessel diameter data 830,and blood pressure data 840 are stored in the storage section 800 asdata.

The correction process data 820 is data where the correction resultsfrom the correction section 150 are stored, and the pressurizationsetting 821 which is the setting of the pressure which is searched forby the pressure search section 151 and the correlation formula 823 whichsets the correlation characteristics of blood vessel diameter and bloodpressure are included in this.

The blood vessel diameter data 830 is data where the blood vesseldiameter of the measurement target blood vessel which is measured by theblood vessel diameter measurement section 110 is stored. The contractionphase blood vessel diameter and the extension phase blood vesseldiameter are included in this.

The blood pressure data 840 is data where the blood pressure of themeasurement target blood vessel which is calculated by the bloodpressure calculation section 160 is stored. The contraction phase bloodpressure and the extension phase blood pressure are included in this.

4. Process Flow

FIG. 6 is a flow chart illustrating the flow of the main process whichis executed by the processing section 100 in accordance with the mainprogram 810 which is stored in the storage section 800.

To begin with, the sending and receiving control section 120 startssending and receiving control of the ultrasound from the ultrasoundsensor 21 (step A1). Then, the processing section 100 performs aninstruction for mounting the cuff type blood pressure monitor 3 withregard to the patient (step A3).

The instruction for mounting the cuff type blood pressure monitor 3 canbe realized by displaying a message which prompts a mounting instructionon the display section 300 or can be realized by there being audiooutput of voice guidance or a predetermined generation of sound whichprompts a mounting instruction from the audio output section 400. Thepatient can be notified by controlling a predetermined lamp to light upor to flash.

Next, the processing section 100 performs the correction process inaccordance with the correction program 811 which is stored in thestorage section 800 (step A5).

FIG. 7 is a flow chart illustrating the flow of the correction process.To being with, the correction section 150 acquires the contraction phaseblood pressure “Ps” and the extension phase blood pressure “Pd” from thecuff type blood pressure monitor 3 via the communication section 500 andstores the contraction phase blood pressure “Ps” and the extension phaseblood pressure “Pd” in the storage section 800 (step B1). Then, thecorrection section 150 carries out the initial setting of thepressurization setting 821 (step B3). Specifically, an initial value of,for example, 10 [mmHg] is set as the pressurization force of thepressurizing section 30.

Next, the pressure search section 151 makes the pressurization controlsection 140 execute control of the pressurization of the pressurizingsection 30 (step B5). The blood vessel diameter calculation section 130calculates the blood vessel diameter of the measurement target bloodvessel from an arrival time difference of the reflected waves from thefront wall and the back wall of the measurement target blood vessel(step B7). At this time, each of the contraction phase blood vesseldiameter “Ds” and the extension phase blood vessel diameter “Dd” arecalculated by tracking the variation in the blood vessel diameteraccompanying a pulsation.

Next, the pressure search section 151 calculates a blood vessel diametervariation width “ΔD” by subtracting the contraction phase blood vesseldiameter “Ds” which is calculated in step B7 from the extension phaseblood vessel diameter “Dd” (step B9). Then, the pressure search section151 determines whether the blood vessel diameter variation width “ΔD”exceeds a predetermined variation width threshold “θ” (step B11). It ispossible to set the variation width threshold “θ” based on therelationship between the pulse pressure (the difference in thecontraction phase blood pressure and the extension phase blood pressure)and the variation width of the blood vessel diameter accompanying apulsation.

In a case where it is determined in step B11 that the blood vesseldiameter variation width “ΔD” does not exceed the variation widththreshold “θ” (step B11; No), the pressure search section 151 changesthe pressurization setting 821 (step B13). For example, a pressure where10 [mmHg] is added to the setting value of the current pressurizationforce is set as a new pressurization force. Then, the pressure searchsection 151 returns the process to step B5.

On the other hand, in a case where it is determined in step B11 that theblood vessel diameter variation width “ΔD” does exceed the variationwidth threshold “θ” (step B11; Yes), the pressure search section 151stores the current pressurization setting 821 in the correction data 820in the storage section 800 (step B15). The series of processes from stepB3 to step B15 are equivalent to a pressure search process which isperformed by the pressure search section 151.

Next, the correction section 150 decides on the correlation formula 823of formula (1) using the contraction phase blood pressure “Ps” and theextension phase blood pressure “Pd” which are acquired from the cufftype blood pressure monitor 3 in step B1 and the latest values for thecontraction phase blood vessel diameter “Ds” and the extension phaseblood vessel diameter “Dd” which are acquired in step B7, and thecorrelation formula is stored in the correction data 820 (step B17).Then, the processing section 100 terminates the correction process.

Returning to the main process of FIG. 6, after the correction processhas been completed, the processing section 100 performs an instructionfor removal of the cuff type blood pressure monitor 3 with regard to thepatient (step A7). It is possible for the instruction for the removal ofthe cuff type blood pressure monitor 3 to be performed with regard tothe patient using a technique which is similar to the instruction forthe mounting of the cuff type blood pressure monitor in step A3.

Next, the processing section 100 calculates the blood vessel diameter“D” based on the ultrasound reflected wave and stores the blood vesseldiameter “D” in the blood vessel diameter 830 of the storage section 800(step A9). Then, the processing section 100 calculates the bloodpressure “P” using the correlation formula 823 which is stored in thestorage section 800 and the blood vessel diameter “D” which iscalculated in step A9 and stores the blood pressure “P” in the bloodpressure data 840 of the storage section 800 (step A11). The processingsection 100 updates the display of the display section 300 using theblood pressure “P” which has been calculated (step A13).

Next, the processing section 100 determines whether the measurement ofblood pressure is complete (step A15), and in a case where it isdetermined that the measurement has not yet been completed (step A15;No), it is determined whether it is a correction timing (step A17). Asthe correction timing in this case, the setting of various timings arepossible. For example, a case where a measurement timing of the timersection 600 becomes a timing which is set in advance (for example, 8o'clock in the morning) can be determined to be the correction timing.

If it is determined that it is the correction timing (step A17; Yes),the processing section 100 returns the process to step A3. Then, thecorrection process using the cuff type blood pressure monitor 3 isexecuted again. In addition, if it is determined that it is not thecorrection timing (step A17; No), the processing section 100 returns theprocess to step A9. Then, the calculation of the blood pressure incontinued.

On the other hand, in a case where it is determined in step A15 that themeasurement has been completed (step A15; Yes), the processing section100 terminates the main process.

5. Action Effects

In the ultrasound blood pressure monitor 1, the blood vessel diametermeasurement section 110 measures the blood vessel diameter of the radialartery which is the measurement target based on the reception results ofthe ultrasound from the ultrasound sensor 21. In addition, thepressurizing section 30 adds a pressure from the body surface so thatthe radial artery is pressed. Then, the correlation formula 823, whichexpresses the relationship between blood vessel diameter and bloodpressure of the radial artery under pressurization by the pressurizingsection 30, is found and stored in the storage section 800. Then, theblood pressure calculation section 160 calculates the blood pressure bycontrolling the pressurization operation of the pressurizing section 30using the blood vessel diameter which is measured under pressurizationand the storage data in the storage section 800.

As is described in the principles, the variation width of the bloodvessel diameter accompanying a pulsation increases with regard to thesame change in blood pressure when the pressure is added from the bodysurface so that the radial artery is pressed compared to when there isno pressurization. Accordingly, it is possible to reduce the effect oferror in the blood vessel diameter measurement by performingpressurization. That is, it is possible to improve the degree ofaccuracy in blood pressure calculation by increasing the change in bloodpressure with regard to the variation in blood vessel diameter due topressurization.

In the embodiment, the pressure search section 151 searches for thepressure, where the variation width of the blood vessel diameteraccompanying a pulsation which is measured by the blood vessel diametermeasurement section 110 satisfies the predetermined condition, bycontrolling the pressure due to the pressurizing section 30 so as tochange. In detail, the pressure is searched for so that the variationwidth of the blood vessel diameter accompanying a pulsation which ismeasured by the blood vessel diameter measurement section 110 exceedsthe predetermined variation width threshold which is set based on therelationship between the pulse pressure and the variation width. Due tothis, it is possible to adjust the pressure which is used inpressurization by the pressurizing section 30.

The storage section 800 stores the correction formula 823 whichindicates the relationship between blood vessel diameter and bloodpressure of the artery in a state of pressurization with the pressurewhich is searched for by the pressure search section 151. Then, theblood pressure calculation section 160 calculates the blood pressure ofthe patient in a state where the pressurization of the pressurizingsection 30 is controlled so that there is pressurization with thepressure which is searched for by the pressure search section 151. Therelationship between blood vessel diameter and blood pressure, in a casewhere control of the pressurization by the pressurizing section 30 wasperformed with the pressure which is searched for by the pressure searchsection 151, is stored as data, and it is possible to correctlycalculate the blood pressure of the patient by using the blood vesseldiameter which is measured in a state of pressurization with thepressure which is the same as the pressure which is searched for by thepressure search section 151 and the correlation formula 823 which isstored in the storage section 800.

6. Modified Example

Naturally, the embodiments where it is possible for the invention to beapplied are not limited to the embodiment described above andappropriate changes are possible in a scope which does not depart fromthe gist of the invention. Below, modified examples will be described.

6-1. Measurement Target Artery

In the embodiment described above, the artery which is the measurementtarget is described as the radial artery in the wrist, but naturally,arteries other than this can be the artery which is the measurementtarget. Since the technique of the embodiment is particularly effectivein a case where a blood vessel which is relatively tough is themeasurement target, for example, a limb artery other than the radialartery can be the measurement target artery.

6-2. Method for Measuring Blood Vessel Diameter

In the embodiment described above, the method for measuring the bloodvessel diameter is described as a measuring method which usesultrasound, but naturally, the method for measuring the blood flow speedis not limited to this. For example, a technique can be adopted wherelight of a predetermined wavelength is irradiated from a light emittingelement toward the artery which is the measurement target andmeasurement of blood vessel diameter is performed based on the reflectedlight.

6-3. Ultrasound Blood Pressure Monitor

In the embodiment described above, the ultrasound blood pressure monitor1 which is used by being mounted onto the wrist of the patient isdescribed as an example, but there can be an ultrasound blood pressuremonitor which is used by, for example, being wrapped around the upperarm. In this case, for example, a configuration is possible where theblood pressure is measured by mounting the ultrasound blood pressuremonitor on the upper arm of one arm and the blood pressure is measuredby mounting the cuff type blood pressure monitor on the upper arm of theother arm. A specific embodiment in this case (referred to below as asecond embodiment) will be described below.

FIG. 8 is a diagram illustrating an example of a configuration of ablood pressure measurement system according to the second embodiment. Inthe blood pressure measurement system, an ultrasound blood pressuremonitor 2 is mounted on the upper arm of one arm of the patient and thecuff type blood pressure monitor 3 is mounted on the upper arm of theother arm of the patient. The ultrasound blood pressure monitor 2 has aconfiguration which is basically the same as the ultrasound bloodpressure monitor 1, but is configured to be provided with a cuff bandand a pressurizing section 30X, which has a pressurizing mechanism forpressurization of the upper arm by sending air into the cuff band,instead of the pressurizing section 30 of the ultrasound blood pressuremonitor 1 and so that it is possible to pressurize the upper arm of thepatient in a uniform manner.

In the second embodiment, the ultrasound blood pressure monitor 2measures the blood vessel diameter of the upper arm artery usingultrasound in a state where the upper arm is pressurized with apressurization force “Po” for correction (referred to below as“correction pressurization force”). Since there are changes in adifference in the inner and outer pressure which is applied to the bloodvessel measured using cuff pressure, the value of the stiffnessparameter “β” is calculated in accordance with formula (2) using theblood vessel diameter which is measured and the blood pressure which ismeasured using the cuff type blood pressure monitor 3.

β=In[(Ps/Po)/(Pd−Po)]/(Ds/Dd−1)  (2)

In addition, during normal measurement after correction, the ultrasoundblood pressure monitor 2 measures the blood vessel diameter of the upperarm artery using ultrasound in a state of pressurization of the upperarm under a pressurization force “Po′” for normal measurement (which isdescribed below as “normal measurement pressurization force”). Then, theblood pressure is calculated from the blood vessel diameter of the upperarm artery in accordance with the correlation formula of formula (3).

P=Pd·exp[β(D/Dd−1)]+Po′  (3)

It is possible to ignore the effect of the change in shape of the bloodvessel since the ultrasound blood pressure monitor 2 presses the upperarm artery of the patient in a uniform manner. As a result, it is notnecessary for the correction pressurization force “Po” and the normalmeasurement pressurization force “Po′” to be the same pressure and thepressures can be arbitrary pressures. Accordingly, it is possible toincrease the degree of accuracy in blood vessel diameter measurement,and subsequently, the degree of accuracy in blood pressure calculationby setting the normal measurement pressurization force “Po′” as apressure so that it is possible to increase the blood vessel diametervariation width. The normal measurement pressurization force “Po′” canbe, for example, approximately 10 mmHg to 50 mmHg, and moreappropriately, approximately 20 mmHg to 30 mmHg.

FIG. 9 is a diagram illustrating an example of changes in the variationwidth of the blood vessel diameter accompanying a pulsation in a casewhere the upper arm artery is pressurized. The horizontal axis isexternal pressure (the units are mmHg) and the vertical axis is bloodvessel diameter variation width (the units are mm). From FIG. 9, it isunderstood that the blood vessel diameter variation width increases asthe external pressure increases.

FIG. 10 is a diagram for describing effects of the blood pressuremeasurement method. The amounts of variation in blood vessel diameterare respectively shown by plotting in a case where the external pressureis 0 mmHg and in a case where the external pressure is 30 mmHg. Thehorizontal axis is blood vessel diameter (the units are mm) and thevertical axis is blood pressure (the units are mmHg). In addition, thecurve which is shown by a solid line is a correlation formula which isgiven by formula (3). Compared to the amount of variation in bloodvessel diameter of approximately 80 μm in a case where the externalpressure is 0 mmHg, the amount of variation in blood vessel diameter isdouble at approximately 160 μm by applying the external pressure of 30mmHg. Accordingly, the degree of accuracy of measurement is simplydoubled since measurement is possible in a state where the size of themeasurement target object is double.

FIG. 11 is a flow chart where a portion of a second main process, whichis executed by the processing section 100 of the ultrasound bloodpressure monitor 2 in the second embodiment instead of the main processof FIG. 6, is extracted. Here, repetitive description is omitted bygiving the same reference numerals to the same steps in the mainprocess.

In the correction process, the value of the stiffness parameter “β” iscalculated in accordance with formula (2) (step C5). After theinstruction for the removal of the cuff type blood pressure monitor 3has been carried out (step A7), the processing section 100 determineswhether it is setting timing of the normal measurement pressurizationforce (step C7). For example, it is determined to be the setting timingin a case where the setting of the normal measurement pressurizationforce has been instructed by the user via the operating section 200 andin a case where a predetermined period of time (for example, one day)has elapsed from the performing of the last setting of the normalmeasurement pressurization force. In a case where it is determined tonot be the setting timing (step C7; No), the process moves to step C23.

On the other hand, in a case where it is determined to not be thesetting timing (step C7; Yes), the processing section 100 determines thesetting method for the normal measurement pressurization force (stepC9). In the setting method, there are the two types of an automaticsetting and a user setting, and for example, the user selects either ofthe setting methods. In a case where the setting method which has beenselected is the user setting (step C9; user setting), the processingsection 100 sets the pressurization force which has been selected by theuser as the normal measurement pressurization force (step C11). Then,the process moves to step C23. On the other hand, in a case where thesetting method which has been selected is the automatic setting (stepC9; automatic setting), the processing section 100 performs a normalmeasurement pressurization force setting process (steps C13 to C21).

Specifically, a predetermined initial value (for example, 10 mmHg) isinitially set as the pressurization force (step C13) and the bloodvessel diameter is measured for a predetermined number of pulsations(for example, 10 to 20 pulsations) using ultrasound in a state ofpressurization with the pressurization force (step C15). Then,dispersion in the blood vessel diameter which has been measured isdetermined (step C17). It is possible to realize the determination ofdispersion by, for example, calculating an average value and a standarddeviation of the extension phase blood vessel diameter for apredetermined number of pulsations and by determining whether thestandard deviation is less than a predetermined threshold. Here, thecontraction phase blood vessel diameter can be used instead of theextension phase blood vessel diameter.

If it determined that the dispersion of the blood vessel diameter islarge (step C17; large), the processing section 100 changes thepressurization force by addition of a predetermined value (for example,5 mmHg) to the setting value of the current pressurization force or thelike (step C19). Then, the process returns to step C15. On the otherhand, if it determined that the dispersion of the blood vessel diameteris small (step C17; small), the current pressurization force is set asthe normal measurement pressurization force (step C21). The series ofprocesses of step C13 to C21 is equivalent to a process where there issearching for a pressure where the blood vessel diameter which ismeasured by the blood vessel diameter measurement section satisfies apredetermined stability condition, and in this case, the processingsection 100 functions as a second pressure search section.

After step C21, the processing section 100 measures the blood vesseldiameter D with the normal measurement pressurization force which hasbeen set in the normal measurement pressurization force setting process(step C23). That is, the blood vessel diameter D is measured usingultrasound in a state where the pressurization of the pressurizingsection 30 is controlled so as to pressurize with the pressure which hasbeen searched for by the second search section. If the measurement iscomplete, the pressurization operation is halted (step C25). Then, theblood pressure P is calculated in accordance with formula (3) using thecorrelation formula which is found in the correction process and theblood vessel diameter D which has been measured (step C27). Then, theprocess moves to step A13 in FIG. 6.

Here, in the embodiment described above, it is not necessary for theultrasound blood pressure monitor 1 and the cuff type blood pressuremonitor 3 to perform measurement by being mounted on the same arm. Bythe ultrasound blood pressure monitor 1 and the cuff type blood pressuremonitor 3 being mounted on different arms, the contraction phase bloodpressure and the extension phase blood pressure can be measured usingthe cuff type blood pressure monitor 3 which is mounted on one of thearms and the contraction phase blood vessel diameter and the extensionphase blood vessel diameter can be measured in a continuous manner usingthe ultrasound blood pressure monitor 1 which is mounted on the otherarm.

In the same manner, in the second embodiment described above, it is notnecessary for the ultrasound blood pressure monitor 2 and the cuff typeblood pressure monitor 3 to perform measurement by being mounted ondifferent arms. For example, the measurement can be performed by theultrasound blood pressure monitor 2 being mounted on the upper arm ofone of the arms and the cuff type blood pressure monitor 3 which isconfigured as a wrist type of blood pressure monitor being mounted onthe wrist of the same arm.

In addition, in the second embodiment, the ultrasound blood pressuremonitor 2 and the cuff type blood pressure monitor 3 can both have apressurizing mechanism using a cuff. As a result, it is possible for theultrasound blood pressure monitor 2 and the cuff type blood pressuremonitor 3 to be configured integrally. In this case, the blood pressureis measured using an oscillometric method by pressurization so thatthere is expulsion of blood from the upper arm using the cuff duringcorrection. In addition, the blood vessel diameter of the upper armartery is measured using ultrasound in a state of pressurization of theupper arm with the correction pressurization force “Po”. Then, it issufficient if the value of the stiffness parameter is calculated inaccordance with formula (2) using the blood pressure measurement valueand the blood vessel diameter measurement value.

In addition, it is possible to appropriately correct the correlationformula by carrying out processing to average each of the contractionphase blood vessel diameter and the extension phase blood vesseldiameter which have been measured continuously and deciding on thecorrelation formula using the average value of the contraction phaseblood vessel diameter and the average value of the extension phase bloodvessel diameter. It is possible to further improve the degree ofaccuracy of blood pressure calculation by calculating the blood pressureusing the correlation formula which has been found in this manner.

6-4. Correlation Characteristics

In the embodiment described above, the case of applying the correlationformula which is expressed by formula (1) as the correlation formulawhich expresses the correlation characteristics of blood vessel diameterand blood pressure is described as an example, but other than this,naturally, correlation formulae where blood vessel diameter and bloodpressure are approximated using a linear relationship and correlationformulae where blood vessel diameter and blood pressure are approximatedusing a non-linear relationship other than formula (1) can be applied.

In addition, naturally, it is not necessary for data on the correlationcharacteristics which is stored in the storage section to be data on thecorrelation formula and such can be data where the correlationcharacteristics of blood vessel diameter pressure and blood pressure areset in a table format (a lookup table).

6-5. Correction Timing

In the embodiment described above, there is description where thecorrection process is performed at the timing which is an initial timeof blood pressure measurement or is a timing which has been decided, butit is possible for the correction timing to be arbitrarily set. Forexample, there are cases where the shape of the measurement target bloodvessel of the patient changes due to a rapid change in air temperature.Therefore, air temperature during the measurement of blood pressure canbe stored and the correction process can be performed with a timing,where a difference in temperature of air temperature during the previousmeasurement and air temperature during the current measurement exceeds apredetermined threshold, as the correction timing.

6-6. Communication Method

In addition, in the embodiment described above, the communication methodof the ultrasound blood pressure monitor 1 and the cuff type bloodpressure monitor 3 is set as wireless communication, but can be wiredcommunication by connection using a cable. In addition, the measurementof blood pressure can be performed by the patient using the cuff typeblood pressure monitor 3 and the measurement value can be input by handinto the ultrasound blood pressure monitor 1 by the patient.

What is claimed is:
 1. A blood pressure measurement apparatuscomprising: a blood vessel diameter measurement section which measuresblood vessel diameter of an artery which is a measurement target; apressurizing section which adds pressure from a body surface so that theartery is pressed; a storage section which stores a relationship betweenblood vessel diameter and blood pressure of the artery underpressurization by the pressurizing section; and a blood pressurecalculation section which calculates blood pressure by controlling apressurization operation of the pressuring section using the bloodvessel diameter, which is measured by the blood vessel diametermeasurement section under pressurization, and storage data in thestorage section.
 2. The blood pressure measurement apparatus accordingto claim 1, further comprising: a first pressure search section whichsearches for a pressure by controlling the pressure due to thepressurizing section so as to change so that the variation width in theblood vessel diameter accompanying a pulsation, which is measured by theblood vessel diameter measurement section, satisfies a predeterminedcondition, wherein the storage section stores the relationship betweenthe blood vessel diameter and the blood pressure of the artery in astate of pressurization with the pressure which has been searched for bythe first pressure search section, and the blood pressure calculationsection controls the pressurization operation of the pressurizingsection so that there is pressurization with the pressure which issearched for by the first pressure search section.
 3. The blood pressuremeasurement apparatus according to claim 2, wherein the first pressuresearch section searches for a pressure where the variation width of theblood vessel diameter accompanying a pulsation, which is measured by theblood vessel diameter measurement section, exceeds a predeterminedvariation width threshold which is set based on the relation of pulsepressure and the variation width.
 4. The blood pressure measurementapparatus according to claim 1, wherein the blood pressure calculationsection controls the pressurization operation of the pressurizingsection so as to pressurize with an arbitrary pressure.
 5. The bloodpressure measurement apparatus according to claim 4, further comprising:a second pressure search section which searches for a pressure bycontrolling the pressurization by the pressurizing section so as tochange so that the blood vessel diameter which is measured by the bloodvessel diameter measurement section satisfies a predetermined stabilitycondition, wherein the blood pressure calculation section controls thepressurization of the pressurizing section so that there ispressurization with the pressure which is searched for by the secondpressure search section.
 6. A blood pressure measurement method for ablood pressure measurement apparatus which is provided with apressurizing section which adds pressure from a body surface so that anartery which is a measurement target is pressed and a storage sectionwhich stores the relationship between blood vessel diameter and bloodpressure of the artery under pressurization by the pressurizing section,the method comprising: measuring blood vessel diameter of the artery;and calculating blood pressure by controlling a pressurization operationof the pressuring section using the blood vessel diameter underpressurization and storage data in the storage section.